<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Title</title>
  <style>
    div {
      width: 400px;
      height: 400px;
      /*background-color: pink;*/
      background-color: rgba(0, 0, 0, 0.5);
    }
  </style>
</head>
<body>

<div>div</div>



</body>
</html>
